Eff ect of prescribed burning on the small-scale spatial heterogeneity of soil microbial biomass in Pinus koraiensis and Quercus mongolica forests of China

Prescribed burning can alter soil microbial activity and spatially redistribute soil nutrient elements.However,no systematic,in-depth studies have investigated the impact of prescribed burning on the spatial patterns of soil microbial biomass in temperate forest ecosystems in Northeast China.The present study investigated the impacts of prescribed burning on the small-scale spatial heterogeneity of microbial biomass carbon(MBC)and microbial biomass nitrogen(MBN)in the upper(0–10 cm)and lower(10–20 cm)soil layers in Pinus koraiensis and Quercus mongolica forests and explored the factors that infl uence spatial variations of these variables after prescribed burning.Our results showed that,MBC declined by approximately 30%in the 10–20 cm soil layer in the Q.mongolica forest,where there were no signifi cant eff ects on the soil MBC and MBN contents of the P.koraiensis forest(p>0.05)after prescribed burning.Compared to the MBC of the Q.mongolica forest before the prescribed burn,MBC spatial dependence in the upper and lower soil layers was approximately 7%and 2%higher,respectively.After the prescribed burn,MBN spatial dependence in the upper and lower soil layers in the P.koraiensis forest was approximately 1%and 13%lower,respectively,than that before the burn,and the MBC spatial variability in the 0–10 cm soil layer in the two forest types was explained by the soil moisture content(SMC),whereas the MBN spatial variability in the 0–10 cm soil layer in the two forests was explained by the soil pH and nitrate nitrogen(NO_(3)^(–)-N),respectively.In the lower soil layer(10–20 cm)of the Q.mongolica forest,elevation and ammonium nitrogen(NH 4+-N)were the main factors aff ecting the spatial variability of MBC and MBN,respectively.In the 10–20 cm soil layer of the P.koraiensis forest,NO_(3)^(–)-N and slope were the main factors aff ecting the spatial variability of MBC and MBN,respectively,after the burn.The spatial distributions of MBC and MBN in the two forests were largely structured with higher spatial autocorrelation(relative structural variance C/[C 0+C]>0.75).However,the factors infl uencing the spatial variability of MBC and MBN in the two forest types were not consistent between the upper and lower soil layers with prescribed burning.These fi ndings have important implications for developing sustainable management and conservation policies for forest ecosystems.

Effects of Spring Biomass Burning in the Indochina Peninsula on May Precipitation in South China

Each year, during the dry season that precedes the summer wind and rainfall Indo-China Peninsula (ICP), significant biomass burning occurs and reaches its peak from March to April. This biomass burning generates large amounts of aerosols that impact East Asia and surrounding areas through the Asian monsoon. This study aims to investigate the potential connection between biomass burning over the ICP and precipitation in South China during May, along with the physical processes involved. The analysis is based on GLDAS soil moisture reanalysis data and CPC (NOAA) precipitation data covering the period from 1980 to 2021. The research findings indicate a negative (positive) correlation between biomass burning in the ICP region during spring and precipitation in the same region (South China) during May. The circulation patterns corresponding to years with biomass-burning emission anomalies are further investigated, and the impact of biomass-burning emissions in spring on soil moisture and temperature is examined. The results suggest that biomass-burning emissions can significantly affect atmospheric circulation and precipitation, ultimately leading to anomalous precipitation in South China.

Estimation of the impact of biomass burning based on regional transport of PM_(2.5) in the Colombian Caribbean

Deterioration of air quality due to the increase in atmospheric emissions from biomass burning(BB)is one of the major environmental problems worldwide.In this study,we estimated the contributions of BB to PM_(2.5) concentrations in the municipalities of Soledad and Malambo located in the Colombian Caribbean.The evaluation period ranged from February 24 to March 30,2018,a period with a high number of BB events recorded in the surroundings of the evaluated sites.The contribution of BB to the two sampling sites was estimated using the Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT)dispersion model with forwarding trajectories from each of the burning points identified by satellite images(n=1089).The PM_(2.5) emissions were determined using the fire radiative power(FRP),obtained by remote-sensing data,and corresponded to the radiant energy released per time unit by burning vegetation.The average PM_(2.5) concentrations during the evaluation period were 19.91μg/m^(3) for Soledad and 22.44μg/m^(3) for Malambo.The average contribution of BB to these municipalities was 22.8%and 28.8%,respectively.The methodology used in this study allowed to estimate the contribution of this important source without knowledge of a previous tracer of BB,thereby increasing the use of the proposed procedure worldwide.This information would enable the implementation of effective mitigation,thereby diminishing the adverse impact of PM_(2.5) on the health of the population.

Spatial and temporal variability of open biomass burning in Northeast China from 2003 to 2017

Open biomass burning(OBB)has a significant impact on the heavy haze pollution in Northeast China(NEC)in recent years,which requires the investigation of the spatiotemporal variations of OBB with different vegetation types to better monitor and control OBB in NEC.The MODIS C6 fire and land cover products,together with the emissions inventory from the Global Fire Assimilation System,were used in this study.The changes in the total number of MODIS fire points in NEC from 2003 to 2017 demonstrated a fluctuating but generally rising trend,with a peak during 2013–2017.Most fire points concentrated in two key periods,i.e.March–April(37%)and October–November(46%).The total number of crop residue burnings in March–April was basically slightly fluctuating and increased sharply from 2013,whilst the number in October–November had a fluctuating and upward trend until 2015,when a decline appeared.The amount of OBB in March–April was higher than that in October–November during 2016–17.OBB in Heilongjiang Province comprised a major proportion of all fires,which accounted for 70.7%from 2003 to 2017;however,the proportion was only 66.2%during 2013–2017.The largest proportion of all fires was in cropland(90.8%),then forest(5.3%)and grassland(3.1%).The cumulative emissions of fine particulate matter,nitrogen oxides,and ammonia from agricultural open burning in NEC reached 78.43 Gg,24.9 Gg,and 13.7 Gg for March–April during 2013–17,respectively,which were close to those in October–November.

Influence of South Asian Biomass Burning on Ozone and Aerosol Concentrations Over the Tibetan Plateau

In this work,the influence of South Asian biomass burning emissions on O_(3) and PM_(2.5)concentrations over the Tibetan Plateau(TP)is investigated by using the regional climate chemistry transport model WRF-Chem.The simulation is validated by comparing meteorological fields and pollutant concentrations against in situ observations and gridded datasets,providing a clear perspective on the spatiotemporal variations of O_(3) and PM_(2.5)concentrations across the Indian subcontinent,including the Tibetan Plateau.Further sensitivity simulations and analyses show that emissions from South Asian biomass burning mainly affect local O_(3) concentrations.For example,contribution ratios were up to 20%in the Indo-Gangetic Plain during the pre-monsoon season but below 1%over the TP throughout the year 2016.In contrast,South Asian biomass burning emissions contributed more than 60%of PM_(2.5)concentration over the TP during the pre-monsoon season via significant contribution of primary PM_(2.5)components(black carbon and organic carbon)in western India that were lofted to the TP by westerly winds.Therefore,it is suggested that cutting emissions from South Asian biomass burning is necessary to alleviate aerosol pollution over the TP,especially during the pre-monsoon season.

On the determination of nitrous oxide emission factor during biomass burning

The emission factors of nitrous oxide have been determined during the combustion of rice straws, maize stalks and wheat stalks in an enclosed combustion system. They equal to 84.4 ± 6.08g/t for rice straws,132± 8.63g/t for maize stalks,and 27.3 ±1.79g/tfor wheat stalks,respectively. The uncertainties in the determination of nitrous oxide have been discussed. The N_2O-N(nitrogen in nitrous oxide emission)accounts for 0. 59% and 0. 87% of the total nitrogen in rice straws and maize stalks,respectively. An 1￣0 ×1￣0 grid map on the distribution of N_2O emission from biomass burning in China mainland was shown.

Once upon a time biomass burning in the western Alps: Nesting effects of climate and local drivers on long-term subalpine fires

Background:The present article questions the relative importance of local-and large-scale processes on the long-term dynamics of fire in the subalpine belt in the western Alps.The study is based on soil charcoal dating and identification,several study sites in contrasting environmental conditions,and sampling of soil charcoal along the elevation gradient of each site.Based on local differences in biomass combustion,we hypothesize that local-scale or landscape-scale processes have driven the fire history,while combustion homogeneity supports the hypothesis of the importance of large-scale or macro-ecological processes,especially climate.Results:Biomass burning during the Holocene resulted from the nesting effects of climate,land use,and altitude,but was little influenced by slope exposure(north versus south),soil(dryness,pH,depth),and vegetation.The mid-Holocene(6500–2700 cal BP)was an important period for climate-driven biomass burning in the subalpine ecosystems of the western Alps,while fires over the last 2500 years appear much more episodic,prompting us to speculate that human activity has played a vital role in their occurrence.Conclusion:Our working hypothesis that the strength of local drivers should offset the effects of regional climate is not validated.The homogeneity of the fire regime between sites thus underscores that climate was the main driver during the Holocene of the western Alps.Long-term subalpine fires are controlled by climate at the millennial scale.Local conditions matter for little in determining variability at the century scale.The mid-Holocene was a chief period for climatic biomass burning in the subalpine zone,while fires during the late Holocene appear much more episodic,suggesting that social drivers has exercised key function on their control.

Emission of Carbonaceous Species from Biomass Burning in the Traditional Rural Cooking Stove in Bangladesh

Characterization of carbonaceous species from the particulate matters (PM) after combustion of seven commonly used biomass species, albizia tree (Albizia julibrissin), dry leaves (mahogany tree), jackfruit tree (Artocarpus heterophyllus), rain tree (Samanea saman), mahogany tree (Swietenia mahogany), cow dung and mango tree (Mangifer aindica) was done. PM samples were collected on quartz fiber filters emitted from biomass burning in a typical rural cooking stove. PM loaded filters were characterized with scanning electron microscope (SEM) for surface morphology, fourier transform infrared (FTIR) to determine the functional group of organic compounds. Black carbon (BC) and brown carbon (BrC) concentrations were determined with Aethalometer. A TOC analyzer was used to determine the total organic carbon (TOC) present in the biomass samples. The surface morphology was almost similar for all biomass burning PM samples. The average concentrations of BC and BrC were 5.85 ± 4.40 and 13.0 ± 8.80 μg·m&#453, respectively. The emission factors of BC and BrC were 1.08 ± 0.89 and 2.35 ± 1.67 mg·g&#451, respectively. Concentration of BC was the highest in dry leaves and the lowest in mango tree. The emission factors of the determined biomass followed the sequence-dry leaves of mahogany > albizia tree > jackfruit tree > rain tree > cow dung > mahogany tree > mango tree. PM from mango tree had lower emissions compared to the other biomass species used in this study.

Source apportionment of PM_(2.5)using PMF combined online bulk and single-particle measurements:Contribution of fireworks and biomass burning

Fireworks(FW)could significantly worsen air quality in short term during celebrations.Due to similar tracers with biomass burning(BB),the fast and precise qualification of FW and BB is still challenging.In this study,online bulk and single-particle measurements were combined to investigate the contributions of FW and BB to the overall mass concentrations of PM_(2.5)and specific chemical species by positive matrix factorization(PMF)during the Chinese New Year in Hong Kong in February 2013.With combined information,fresh/aged FW(abundant ^(140)K_(2)NO_(3)^(+)and ^(213)K_(3)SO_(4)^(+)formed from ^(113)K_(2)Cl^(+)discharged by fresh FW)can be extracted from the fresh/aged BB sources,in addition to the Second Aerosol,Vehicles+Road Dust,and Sea Salt factors.The contributions of FW and BB were investigated during three high particle matter episodes influenced by the pollution transported from the Pearl River Delta region.The fresh BB/FW contributed 39.2%and 19.6%to PM_(2.5)during the Lunar Chinese New Year case.However,the contributions of aged FW/BB enhanced in the last two episodes due to the aging process,evidenced by high contributions from secondary aerosols.Generally,the fresh BB/FW showed more significant contributions to nitrate(35.1%and15.0%,respectively)compared with sulfate(25.1%and 5.9%,respectively)and OC(14.8%and11.1%,respectively)on average.In comparison,the aged FW contributed more to sulfate(13.4%).Overall,combining online bulk and single-particle measurement data can combine both instruments’advantages and provide a new perspective for applying source apportionment of aerosols using PMF.

Source profiles of particulate organic matters emitted from cereal straw burnings

Cereal straw is one of the most abundant biomass burned in China but its contribution to fine particulates is not adequately understood. In this study, three main kinds of cereal straws were collected from five grain producing areas in China. Fine particulate matters （PMzs） from the cereal straws subjected to control burnings, both under smoldering and flaming status, were sampled by using a custom made dilution chamber and sampling system in the laboratory. Element carbon （EC） and organic carbon （OC） was analyzed. 141 compounds of organic matters were measured by gas chromatography-mass spectrum （GC-MS）. Source profiles of particulate organic matters emitted from cereal straw burnings were obtained. The results indicated that organic matters contribute a large fraction in fine particulate matters. Levoglucosan had the highest contributions with averagely 4.5% in mass of fine particulates and can be considered as the tracer of biomass burnings. Methyloxylated phenols from lignin degradation also had high concentrations in PM2.5, and contained approximately equal amounts of guaiacyl and syringyl compounds. 13-Sitostrol also made up relatively a large fraction of PMz5 compared with the other sterols （0.18%-0.63% of the total fine particle mass）. Normal alkanes, PAHs, fatty acids, as well as normal alkanols had relatively lower concentrations compared with the compounds mentioned above. Carbon preference index （CPI） of normal alkanes and alkanoic acids showed characteristics of biogenic fuel burnings. Burning status significantly influenced the formations of EC and PAHs. The differences between the emission profiles of straw and wood combustions were displayed by the fingerprint compounds, which may be used to identify the contributions between wood and straw burnings in source apportionment researches.

Effects of combustion temperature on the optical properties of brown carbon from biomass burning

Biomass burning has been known as one of main sources of Brown Carbon(BrC)in atmosphere.In this study,by controlling the combustion temperature at 250℃,350℃,and 450℃,the methanol soluble organic carbon(MSOC)and methanol insoluble carbon(MISC)from pine wood burning was collected by impinger.UV–Vis,excitation emission matrix(EEM),TEM and FTIR spectra were applied to investigate the properties of BrC collected.For MSOC at 250℃ and 350℃,all the spectral profiles of UV–Vis absorption and excitation emission matrix are almost the same,while the EEM of MSOC at 450℃ are different from that of the other two.For MISC fuorescence was observed only in the case of 450℃.In the FTIR spectra,with the temperature increasing the peaks associated to the oxygen-contained functions was weakened,indicating the formation of the fuorophores with larger conjugated system,especially aromatic hydrocarbons.Our results show that biomass combustion at low temperature produces more oxygen-riched BrC,which possesses relatively lower light absorption,while at high temperature produces more aromatics hydrocarbons with relatively strong light absorption.The results of this work are helpful to trace the source of brown carbon and optimize biomass energy utilization.

Pollutant emissions from biomass burning:A review on emission characteristics,environmental impacts,and research perspectives

Biomass is one most abundant resource on the earth providing important energies in support of so-cioeconomic development in many areas.Burning of biomass fuels comprises to nearly 10%of the total energy from anthropogenic combustion processes:however,as the burning is usually incomplete,this process yields products of incomplete combustion posing consequently significant impacts on air quality,human health,and climate change.Here,we analyzed spatiotemporal characteristics in intentional and unintentional biomass burning from different sectors,discussed impacts of biomass burning emissions on indoor and outdoor air quality,and consequent influences on human health.The global total con-sumption amount of biomass including both natural and anthropogenic sources was approximately 7900 Tg in 2019,with significantly large regional and sectorial discrepancies among regions.Globally,anthropogenic biomass burning amounts increased gradually,but notably in some developing countries like China residential consumption of biomass fuels,as one large sector of biomass use,decreased over time.Uncommercial biomass consumption needs to be accurately quantified.There are relatively rich datasets of pollutant emission factors from biomass burning,including laboratory and field tests,but still large variations exit and contribute substantially to the uncertainty in emission inventory.Global pri-mary PM2.5,black carbon and organic carbon emissions from biomass burning were about 51,4.6,and 29 Tg,respectively,contributing to nearly 70%,55%,and 90%of the total emission from all sources,and emissions from the residential sector and open fires are major sources.Brown carbon emissions from biomass burning attracts growing interests but available studies adopted different methodologies challenging the comparability of those results.Biomass burning emissions polluted not only ambient air but more severely indoor air quality,adversely affecting human health.Future studies that should be emphasized and promoted are suggested.

Influence of meteorological factors on open biomass burning at a background site in Northeast China

Biomass burning(BB)is a very important emission source that significantly adversely impacts regional air quality.BB produces a large number of primary organic aerosol(POA)and black carbon(BC).Besides,BB also provides many precursors for secondary organic aerosol(SOA)generation.In this work,the ratio of levoglucosan(LG)to organic carbon(OC)and the fire hotspots map was used to identify the open biomass burning(OBB)events,which occurred in two representative episodes,October 13 to November 30,2020,and April1 to April 30,2021.The ratio of organic aerosol(OA)to reconstructed PM_(2.5)concentration(PM_(2.5)^(*))increased with the increase of LG/OC.When LG/OC ratio is higher than 0.03,the highest OA/PM_(2.5)^(*)ratio can reach 80%,which means the contribution of OBB to OA is crucial.According to the ratio of LG to K^(+),LG to mannosan(MN)and the regional characteristics of Longfengshan,it can be determined that the crop residuals are the main fuel.The occurrence of OBB coincides with farmers’preferred choices,i.e.,burning biomass in“bright weather”.The“bright weather”refers to the meteorological conditions with high temperature,low humidity,and without rain.Meteorological factors indirectly affect regional biomass combustion pollution by influencing farmers’active choices.

Pre-fire aboveground biomass, estimated from LiDAR, spectral and field inventory data, as a major driver of burn severity in maritime pine (Pinus pinaster) ecosystems

Background:The characterization of surface and canopy fuel loadings in fire-prone pine ecosystems is critical for understanding fire behavior and anticipating the most harmful ecological effects of fire.Nevertheless,the joint consideration of both overstory and understory strata in burn severity assessments is often dismissed.The aim of this work was to assess the role of total,overstory and understory pre-fire aboveground biomass(AGB),estimated by means of airborne Light Detection and Ranging(LiDAR)and Landsat data,as drivers of burn severity in a megafire occurred in a pine ecosystem dominated by Pinus pinaster Ait.in the western Mediterranean Basin.Results:Total and overstory AGB were more accurately estimated(R^(2) equal to 0.72 and 0.68,respectively)from LiDAR and spectral data than understory AGB(R^(2)=0.26).Density and height percentile LiDAR metrics for several strata were found to be important predictors of AGB.Burn severity responded markedly and non-linearly to total(R^(2)=0.60)and overstory(R ^(2)=0.53)AGB,whereas the relationship with understory AGB was weaker(R ^(2)=0.21).Nevertheless,the overstory plus understory AGB contribution led to the highest ability to predict burn severity(RMSE=122.46 in dNBR scale),instead of the joint consideration as total AGB(RMSE=158.41).Conclusions:This study novelty evaluated the potential of pre-fire AGB,as a vegetation biophysical property derived from LiDAR,spectral and field plot inventory data,for predicting burn severity,separating the contri-bution of the fuel loads in the understory and overstory strata in Pinus pinaster stands.The evidenced relationships between burn severity and pre-fire AGB distribution in Pinus pinaster stands would allow the implementation of threshold criteria to support decision making in fuel treatments designed to minimize crown fire hazard.

生物质热成烟气溶解性有机质与Cu^(2+)和Cd^(2+)的络合特性及机制研究

由于全球野火的频发和秸秆的肆意焚烧,生物质燃烧产生的溶解性有机质(BBS-DOM)的环境效应备受关注.BBS-DOM最终沉降在水体和土壤环境中,并可改变地表环境中污染物(如重金属)的环境行为和归趋.然而,BBS-DOM与重金属之间的络合特性尚不清楚.本研究通过燃烧苜蓿、松木和玉米秸秆制备不同的BBS-DOM,并选择Cu^(2+)和Cd^(2+)为模型污染物,络合滴定实验、二维同步荧光光谱(2D-SFS-COS)和二维红外光谱(2D-FTIR-COS)研究了BBS-DOM与重金属之间的络合特性.结果表明,BBS-DOM与Cu^(2+)络合优先顺序为类蛋白物质>类腐殖酸物质>多酚类物质,与Cd^(2+)络合优先顺序为多酚类物质和类腐殖酸物质>类蛋白物质.此外,BBS-DOM中官能团与Cu^(2+)和Cd^(2+)的络合顺序因原料类型不同而有所差异.苜蓿燃烧产生的BBS-DOM中官能团与Cu^(2+)和Cd^(2+)络合顺序为芳环C=C>C-O-C/C-O>-C=O,松木和玉米秸秆燃烧产生的BBS-DOM中的-C=O优先与Cu^(2+)络合,而松木燃烧产生的BBS-DOM中的芳环C=C优先与Cd^(2+)络合,玉米秸秆燃烧产生的BBS-DOM与Cd^(2+)的官能团络合顺序为C-O-C/C-O>芳环C=C.此外,本研究还发现Cu^(2+)的加入增加了BBS-DOM的分子大小,可能是因为Cu^(2+)起到桥接作用,将多个BBS-DOM分子聚合成更大的分子.本研究为在分子水平上深入理解BBS-DOM在水环境中与Cu^(2+)和Cd^(2+)络合的机制提供了重要的理论基础,为合理评估BBS-DOM在水环境中的环境效应提供了科学依据.

重庆白市驿PM_(2.5)中糖类特征及来源

大气有机颗粒物是引起大气污染的重要成分之一,而四川盆地典型山地城市大气PM_(2.5)的有机分子示踪物组成及其特征研究相对国内其它热门城市较少.为探究四川盆地典型山地城市大气PM_(2.5)中糖类化合物的特征,利用气相色谱-质谱联用(GC-MS)检测了重庆市白市驿不同季节PM_(2.5)昼夜样品中12种糖类化合物的浓度水平,包括脱水糖、初级糖和糖醇.结果表明:①重庆市白市驿大气PM_(2.5)中脱水糖占总糖的比例超过85%,其中,左旋葡聚糖占比最大.②总糖浓度为(264±208)ng·m^(-3),且白天浓度((226±198)ng·m^(-3))低于晚上浓度((307±212)ng·m^(-3)).③总糖浓度呈现季节差异,夏季((52.5±47.9)ng·m^(-3))<秋季((287±172)ng·m^(-3))<春季((294±206)ng·m^(-3))<冬季((420±176)ng·m^(-3)),主要受到气象条件、民用取暖、植被生长等多因素的影响.④分子标志物源解析结果表明,生物质燃烧(BB-OC)、植物碎屑(P-OC)和真菌孢子(F-OC)排放的有机碳(Organic Carbon,OC)浓度分别为(2166±1711)、(11.7±11.8)和(47.5±36.9)ng·m^(-3)(以C计,下同),其对的OC的贡献分别为16.9%、0.09%和0.53%.

2020年1月哈尔滨PM_(2.5)重污染形成机制

分析2020年1月哈尔滨重污染事件期间PM_(2.5)的化学组成和影响因素,采用后向轨迹聚类和权重潜在源贡献因子法定量评估区域传输对PM_(2.5)的贡献,讨论该重污染事件的形成机制。结果表明:PM_(2.5)重污染事件主要来源于一次排放,其中生物质燃烧的贡献显著,而极低气温(-18.0℃)和高相对湿度(80.0%)条件可显著促进二次气溶胶的生成。基于气团后向轨迹以及权重潜在源贡献因子研究发现,绥化、大庆、长春和松原等周边城市的区域传输对哈尔滨空气质量的影响也不可忽视。

云南及周边地区闪电活动和其他干扰因素对NO_(2)的协同影响

以2018年9月至2022年8月为研究时段,采用多种统计方法对滇西南及周边生物质燃烧高发区(A区)、滇中人类活动强度较大的城市群区(B区)2—4月和6—8月闪电活动及其他干扰因素对NO_(2)的影响进行对比分析。结果表明:①2—4月A、B区NO_(2)柱浓度分别与火点数和人为CO_(2)排放在空间上存在显著正相关,但与闪电次数呈显著负相关。②闪电活动多伴有明显降雨(R≥1 mm),闪电活动较弱时,降雨对地面NO_(2)的湿沉降作用明显,较强的闪电活动下降雨的湿沉降仍无法完全抵消闪电对地面NO_(2)浓度增长的贡献。③6—8月初次出现闪电时A、B区地面NO_(2)浓度前6 h逐时增加,之后3 h则逐时缓慢减小。④闪电日A、B区地面NO_(2)浓度整体高于无闪电日,生物质燃烧强度、降雨强度和大气边界层高度等变化均会对其产生明显影响。

大兴安岭火烧迹地天然次生林土壤微生物生物量及酶活性特征研究

探究火烧迹地植被恢复过程中土壤微生物生物量及酶活性的变化规律,为火烧迹地森林恢复途径选择及恢复成效评价提供科学依据。以大兴安岭重度火烧迹地落叶松母树-白桦林(MB)、林下抚育-白桦林(FB)、无干扰白桦林(BB)3种不同类型的白桦林为研究对象,落叶松人工林(LL)为对照,测定0~5、5~10、10~20 cm土壤微生物生物量碳(MBC)、土壤微生物生物量氮(MBN)和脲酶(URE)、酸性磷酸酶(ACP)、蔗糖酶(SUC)、过氧化氢酶(CAT)活性。结果表明,1)土壤MBC、MBN含量变化为239.16~852.09 mg/kg和37.08~114.99 mg/kg,除10~20 cm土层外MBC、MBN含量由大到小依次为MB、FB、LL、BB。2)MB土壤ACP、CAT和URE活性最高,FB的ACP、SUC、CAT活性均值要高于LL,BB的URE、ACP活性均值低于LL。3)冗余分析表明,0~5 cm土层土壤SOC、SAP、MBN对土壤酶活性的解释率达到了46.8%、24.9%和4.5%,5~10 cm土层土壤NO-3-N、pH、MBC的解释率分别为61.8%、11.4%和4.0%。10~20 cm土层土壤NO-3-N、pH、TN的解释率为53.3%、14.7%和12.4%。研究表明火后保留具有繁殖能力的树木作为母树恢复森林和及时森林抚育管理对土壤微生物生物量和酶活性具有促进作用。

中南半岛春季气溶胶直接辐射强迫时空演变特征分析

中南半岛国家春季存在大量的生物质燃烧活动,生成的气溶胶会通过大气环流影响我国西南地区大气辐射收支,探究其对大气加热率的影响可为研究它对天气和气候的影响提供依据。基于MERRA-2再分析数据中逐时的气溶胶和晴空下的辐射通量等资料,首先分析其时空特征,其次利用EOF、合成分析等统计方法,讨论中南半岛气溶胶光学厚度(AOD)、地表气溶胶直接辐射强迫(ADRF)的时空演变特征及其与大气短波加热率的关系。结果表明:(1)在3-4月生物质燃烧季节,中南半岛与云南省均存在AOD极大值,它们的时间序列变化趋势具有较高的一致性,主要表现为老挝和越南北部地区AOD中心值超过1,受其影响云南省的AOD由北向南逐渐增强。(2)3-4月中南半岛生物质燃烧AOD与总AOD的高值中心一致,说明该区域气溶胶主要来源于生物质燃烧,老挝北部存在高达28 kg·m^(-1)·d^(-1)的生物质燃烧气溶胶的水平通量散度,能将气溶胶向东北方向输送至中国。(3)地表ADRF与AOD时空分布存在较高的一致性,3-4月老挝和越南的北部地区同样存在地表ADRF高值中心,其值可达-36 W·m^(-2)。EOF第一模态中,印度东北角与我国西藏东南部交界处、老挝、越南和泰国地区均为正位相区域,主要在3-4月出现极大值,2017-2018年间极值减弱,2019年再次增大。云南省地表ADRF时间变化趋势与中南半岛变化一致。(4)地表负ADRF和大气短波加热率的统计关系为:地表的净辐射通量减少越多,低层大气吸收短波辐射造成的加热越大,表明大气内气溶胶截留的短波辐射通量越多,该现象在700 hPa上最为明显,尤其是3-4月。